1. Field of the Invention
The present invention relates to a screw feeding device in a continuous screw driving tool and particularly to a screw feeding device for feeding screws carried on a screw carrying belt one by one by moving the screw carrying belt by a distance corresponding to one pitch of the carried screws in response to one cycle of a screw driving operation.
2. Description of the Prior Art
As shown in FIG. 27, the conventional continuous screw driving tool includes a screw feeding device including a casing 61 and a feeder box slidably movable within a feeder box. When the tool is adapted to drive a screw into an article such as a picture frame in a position adjacent a stepped portion D of the article, a lower end 61a of the casing 61 of the screw feeding device may abut on an upper surface of the stepped portion D as the casing 61 is lowered for driving the screw. This may cause a problem that the stepped portion D is damaged by the casing 61.
For preventing the article from such a damage, Japanese Laid-Open Patent Publication Nos. 3-49879 and 4-111781 have proposed to determine an upper stroke end of the feeder box 60 such that the distance between the lower end 61a of the case 61 and a lower end of the feeder box 60 is greater than a predetermined height L0 of the stepped portion D when the feeder box 60 is in its upper stroke end. Here, the height L0 is appropriately selected.
In order to provide such a greater distance, a screw feeding device of the continuous screw driving tool of the above publications has constructed to include a feeding arm 65 which is pivotally mounted on the feeder box 60 as shown in FIG. 28. The feeding arm 65 has one end engaged with a feeding pin 63 extending laterally from a ratchet wheel 62 and has the other end engaged with a guide slot 64 having a bent portion and formed in a lateral surface of the casing 61.
The ratchet wheel 62 is rotatably supported by the feeder box 60 and has a plural number of feeding claws 62a formed on its periphery. With the feeding claws 62a engaged with a screw carrying belt S, the ratchet wheel 62 is rotated in a direction indicated by an arrow in FIG. 28, so that the screw carrying belt S is moved leftwardly by a distance corresponding to one pitch of the screws. Such rotation of the ratchet wheel 62 is produced by the movement of the casing 61 in the downward direction. Thus, as the casing 61 is moved downwardly for driving the screw, the feeding arm 65 is pivoted by a predetermined angle in a counterclockwise direction indicated by an arrow in FIG. 28 due to the movement of the other end of the feeding arm 65 along the guide slot 64, so that the feeding pin 63 in engagement with one end of the feeding arm 65 is forced to be moved in a feeding direction of the screw carrying belt S.
The feeding arm 65 interposed between the ratchet wheel 62 and the casing 61 serves to provide a remote control of the rotation of the ratchet wheel 62 to be caused by the downward movement of the casing 61, so that the lower stroke end of the casing 61 can be determined to prevent the stepped portion D from being damaged while a sufficient stroke of movement of the feeder box 60 relative to the casing 61 can be ensured.
However, with the conventional screw feeding device, one end of the feeding arm 65 is always in engagement with the feeding pin 63 which extends laterally from the ratchet wheel 62. Therefore, one end of the feeding arm 65 as well as the feeding pin 63 tends to be soon worn, so that the conventional screw feeding device still involves the problem that it has less durability.